Mexico's environmental prosecutor Profepa has imposed a new partial order of closure on Grupo Mexico’s (BMV:GMEXICOB) Buenavista copper mine, which polluted waterways with highly toxic waste last month, forcing authorities to restrict water supply to about 800,000 people.

The directive "limits" the mine's copper leaching activities, a chemical process by which metals like copper are separated from ore, but it was unclear how large an impact the order would have on Buenavista’s operations.

Late last month the country’s environment secretary Juan Jose Guerra Abud said the miner gave false information about the toxic spill at the copper mine, located just about 40 km from the U.S. border. He also said his office would file a criminal lawsuit against Grupo Mexico.

Days after the spill Profepa continued to find concentrations of arsenic and some metals that exceeded levels permitted in the waters of Sonora, which prompted it to order a shut-off of water use from the dam for weeks.

The agency said the fine for the spill could reach up to $3 million, or 40 million Mexican pesos.

Top mining state

Sonora is home to more than a quarter of Mexico's mining industry and leads in gold, copper and graphite production.

Mexico's federal government recently opened up the country's vital energy sectors such as electricity generation and oil production to private companies.

In 2009 an American subsidiary of Grupo Mexico, Asarco, paid the U.S. government a record $1.79 billion to settle hazardous waste pollution in 19 states.